The invention relates to a method for estimating a weight or load of clothes in a clothes washer, and a washing machine controller operating using the method, and more specifically to an estimation method employing low cost velocity or position sensors.
The weight of a load of clothes loaded into a clothes washer for washing is an important parameter in determining the proper amount of water and detergent to be used for the wash cycle. Large clothes loads require larger quantities of water than do small loads. Better clothes washability and significant water and energy savings can be achieved when the proper amount of water is filled into the washer tub for a given clothes load. Too much water or detergent is wasteful, and too little of either will generally adversely affect the effectiveness of the washing, and may result in increased energy consumption due to a higher load on the motor as a result of the inability of the clothes to move freely in the water.
Several U.S. patents are directed to estimation of the load of clothes loaded into a washer. Estimation techniques or methods employed by the washer itself are desirable in that it eliminates guesswork on the part of the machine operator which can lead to improper water fill or use of an improper amount of detergent.
Other patents, for example, U.S. Pat. Nos. 4,607,408, 5,577,283, and EU 0345120A1, employ a dynamic model of the basket/clothes and motor in performing clothes load estimation. The dynamic model in the '283 patent, for example, is expressed as: EQU T.sub.b -T.sub.f =(I.sub.c +I.sub.b).alpha..sub.b
where T.sub.b is the torque provided by the motor to the basket, T.sub.f is the frictional torque of the rotational system (that is, basket or drum), I.sub.c and I.sub.b are the moments of inertia of the clothes and basket respectively, and .alpha..sub.b is the angular acceleration of the basket.
The primary limitation of the system of the '283 patent is the assumption that the applied torque (T.sub.b -T.sub.f) is the same regardless of the load size or aging effects of washer parts (such as the clutch mechanism). This assumption can be violated in practice because mechanical components age with usage in unpredictable ways. Therefore, a better load estimation technique, that is robust to variabilities in the applied torque is desirable. In addition, it is desirable to have a low cost implementation of the load sensing approach.